textproduct: Rapid City

KEY MESSAGES

- Increasingly unsettled this weekend with beneficial rainfall for many and the possibility of isolated severe thunderstorms later Saturday. - Elevated fire weather conditions Friday - Cooler temperatures for Sunday through Tuesday, then a gradual warm up for the rest of next week.

UPDATE

Issued at 1027 PM MDT Thu Jun 18 2026

03z surface analysis had weak trough bisecting the CWA in response to compact shortwave energy over central ND. This wave assisted a cluster of thunderstorms under 110kt jet. 00z KUNR sounding was mixed to 540mb with an inverted-V thermo profile which supported a series of convective wind reports across northwestern SD this evening along with a couple of severe thunderstorm warnings. Latest guidance suggests jet will support a few showers overnight from southeast MT into north-central SD with PoPs adjusted. Current forecast in pretty good shape after tonight.

Mostly dry Friday will give way to increasingly unsettled weather for the weekend. Northwest flow aloft will become west as a series of disturbances move through the CWA inducing southeasterly low-level flow and a good fetch of low-level moisture (PWATs rising to 100-150% of normal). Buoyancy Saturday afternoon/evening will be modulated by early Saturday cluster of shra/TS. If atmosphere recovers enough over northeastern WY/southwestern SD, active/severe storms may develop given forecast shear, especially northeast of surface low which will be located over central WY. Chance of QPF by 12z Monday >1.00" is >50% from the Black Hills eastward. Beneficial if it fully materializes for sure.

DISCUSSION

(This Evening Through Thursday) Issued at 155 PM MDT Thu Jun 18 2026

Latest satellite imagery shows continued northwest flow over the CWA. A few showers are starting to dot the landscape but rain amounts will be negligible.

Looking ahead to tonight and tomorrow, we'll continue the chances for isolated showers and non-severe storms trying to drift in from the north and northwest. Temperatures will be near-normal with overnight lows in the 40s to low 50s and afternoon highs in the 70s to low 80s.

Friday night and the weekend will see a weather pattern change that will bring very different weather. The upper level northwesterly flow will shift to a more westerly flow as a high pressure builds over the desert southwest. At the surface, a lee side low looks to develop in eastern Colorado. This pattern will bring rain, and thunderstorms to the central plains, including western South Dakota and northeast Wyoming.

With forecasted PWATs nearing 150% of normal in some models, there is potential for heavy rain. The WPC has put most of western South Dakota and northeast Wyoming in a marginal risk for excessive rainfall. Saturday morning to Monday morning rainfall amounts could be quite impressive; the EURO and GFS ensemble's 75th percentile for Saturday and Sunday rainfall amounts are around 1 to 1.5 inches, heaviest rain in south-central South Dakota. The 25th percentile is around 0.50 to 0.75 inches. So based on that, there is a solid chance for widespread 48 hour rainfall amounts near 1 inch in western South Dakota.

The SPC has a slight risk of severe weather centered over the KS/NE border but the surrounding Marginal Risk does spread into southwestern SD. At this time, main concerns would be gusty winds and hail.

AVIATION

(For the 06Z TAFS Through 06Z Friday Night) Issued At 948 PM MDT Thu Jun 18 2026

VFR conditions are expected through the forecast period. Isolated/scattered shra/TS will continue into the overnight hours across (mainly) northwestern SD and extreme northeastern WY.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.